The present invention relates to a ball linear guide and a method of manufacturing the same.
The ball linear guide is often used for X, Y, and Z axes in machine tools such as numerically controlled (NC) machines, also in other working machines, automatic welders, injection molding machines, automatic conveyance apparatuses, industrial robots, and further in slide portions of general industrial machines.
The ball linear guide is constructed in such a manner that balls circulate continuously through a ball circulation path formed annularly. FIGS. 5A to 5E show a structural example of a conventional ball linear guide, in which FIG. 5A is a top view, FIG. 5B and FIG. 5C are side views in different directions, FIG. 5D is a sectional view taken on line B—B in FIG. 5B, and FIG. 5E is a sectional view (LM (Linear Motion) block end face) taken on line A—A in FIG. 5A.
In these figures, the numeral 51 denotes an LM block (slider) which constitutes a bearing body mounted on a rail, numerals 52 and 53 denote end plates (ball direction changing parts) attached to both ends of the LM block 51 and serving as return U groove ball holders, numerals 54 and 55 denote round pieces (ball direction changing parts) inserted between the LM block 51 and the end plates 52, 53, numeral 56 denotes a mounting screw for mounting the round pieces 54, 55 and the end plates 52, 53 to the LM block 1, numeral 57 denotes a loaded ball groove constituted by a dovetail groove which is formed on a side face opposed to a slide surface of the rail of the LM block 51, numeral 58 denotes an unloaded ball hole formed on the side opposite to the slide surface of the track base of the LM block 51, numeral 59 denotes a ball guiding semicircular portion formed in the round pieces 54 and 55, numeral 60 denotes a direction changing U groove formed in each of the end plates 52 and 53, numeral 61 denotes a ball, numeral 62 denotes a mounting and positioning hole, numeral 63 denotes an end plate/round piece mounting tapped hole, and numeral 64 denotes a tapped hole for mounting the block 51 to a machine or apparatus.
In this conventional ball linear guide, the balls 61 move as loaded balls through the loaded ball groove 57, then, as unloaded balls, change their direction 180° in the direction changing U groove 60 formed in the end plate 52, then move through the unloaded ball hole 58, thereafter again change their direction 180° in the direction changing U groove 60 formed in the end plate 53, and thereafter again return as loaded balls into the loaded ball grooves 57.
Thus, the ball circulation path which comprises the loaded ball groove 57, the unloaded ball groove 58 and the direction changing U groove 60 is in the shape of a field track, in which the portion of the loaded ball groove 57 is easy to be machined from the exterior, but the unloaded ball hole 58 and the direction changing U groove 60 are difficult to be machined from the exterior. Therefore, the end plates 52 and 53 in each of which is formed the LM block 51 with the loaded ball groove 57 and the unloaded ball hole 58 as a linear hole formed therein, and the round pieces 54 and 55 which form the direction changing U groove 60, are fabricated separately and are then combined together to produce a ball linear guide.
Generally, the LM block 51 is constituted by a metallic block, and as the end plates 52 and 53 there are used resinous end plates each formed with a semicircular ball passage. More specifically, in an assembling work, the end plates 52 and 53 having semicircular ball passages are fixed with mounting bolts 56 to both ends of the LM block 51 formed with linear ball. This assembling work is performed through the round pieces (ball guide plates) 54 and 55 made of a synthetic resin at both ends of the LM block 51.
Since this ball linear guide is constituted by a combination of LM block 51, round pieces 54, 55, and end plates 52, 53, division lines are present among them, so in joint portions between the LM block 51 and the end plates 52, 53 there exist chamfered structures based on the difference in height which is caused by joint of the ball passages, i.e., the difference in height between the LM block 51 and the end plates 52, 53. Consequently, there occurs a case where the movement of balls is not always smooth. In this case, a smooth rotation of balls is not obtained, so that it is impossible to effect a high-speed rotation of balls and a loud vibration noise is generated.
Moreover, in point of fabrication, the number of parts is large because of a divided structure, and hence the number of machining steps for the end plates, bolt mounting taps and holes is large and a work for mating bolts and parts is necessary. Thus, the number of working steps is large and close attention is needed for the assembly.
In particular, without the rail, the balls positioned within each of the loaded ball grooves cannot be held within the dovetail groove and fall off from the loaded ball groove. In such a case, handling of the balls is not easy. A technique for preventing this inconvenience has been proposed. According to this proposal, a linear member for preventing the drop of balls is disposed on a front side of the dovetail groove to prevent drop of the balls even when the ball linear guide is pulled out from the rail (see, for example, a known literature 1 (Japanese Unexamined Utility Model Publication No. 137417/1984 (page 1, FIG. 1))).
FIGS. 6A to 6B are explanatory diagrams showing the structure of the proposed technique, in which FIG. 6A is a sectional plan view and FIG. 6B is a sectional view of a principal portion. In the same figure, the same portions as in FIGS. 5A to 5E are identified by the same reference numerals. This structure is different from the structure of FIG. 5 in that a ball dislodgment preventing member 65 constituted by a line of a circular or square section is attached to the front side of the loaded ball groove 57, whereby it is possible to prevent dislodgment of the balls 61 in the aforesaid case.